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X-2
Installation, Operating & Service Manual
11
Operation
(continued)
6. More Information About Adjustable Parameters.
A. High Limit (
HL
_)
Burner turns "off" when boiler water
temperature (
bt
) is above this value.
Operating setpoint (
SP
) equals high limit
setpoint.
B. Differential (
df_
)
Differential is number of degrees boiler
temperature must decrease below the
operating setpoint before boiler can restart.
C. Circulator Overrun Time (
OR_
)
Circulator overrun time (also called “circulator
off delay” or “circulator post purge”) continues
circulator operation after a call for heat has
ended, sending excess heat from boiler into
system.
NOTICE:
Ensure system piping and zone panel
settings allow water flow to priority zone after call
for heat ends.
D. Circulator Pre-purge Time (
PP_
) See Table 11-
5.
When boiler is warm (boiler water temperature
higher than 140°F (adjustable using start
temperature parameter) and there is a
thermostat call for heat, system circulator is
started and boiler firing is delayed Circulator
Pre-purge minutes. If temperature drops below
140°F or there is a DHW call for heat, boiler
is started without delay. Additionally, boiler is
started without delay if thermostat call for heat
is initiated when boiler water temperature is
less than 140°F. This feature helps save energy
by satisfying home heating needs with residual
boiler heat rather than cycling boiler.
E. Start Temperature
(
St_
)
Amount of “heat available” is calculated by
taking difference between measured boiler
water temperature and Start Temperature
setting. Useful “heat available” is dependent
on type of heating emitter installed in home.
Heat emitters require a certain minimum
temperature to operate effectively. Default
settings reflect cast iron radiators. Fan coils
may require a start temperature setting of
180°F or 160°F before providing heat to home.
F. Priority Time (
Pt_
)
When Priority Time parameter is set to “on”
and Domestic Hot Water (DHW) call for heat is
“on”, the DHW demand will take “Priority” over
home heating demand. During Priority Time,
system circulator will be forced “off”. Priority
Time ends and system circulator is released to
service home heating demand when Domestic
Hot Water call for heat is over. When Priority
Time parameter is set to “Off”, DHW call for
heat does not force “off” system circulator.
Table 11-5: Circulator Pre-purge Time example,
(
PP
_
= 2 minutes)
Call for
Heat
Source
DHW
Terminal
Selection
Boiler
Temperature
Burner Status
TT = on
-
<140
Start with no delay
TT = on
-
>140
Start after 2 minute delay
DHW = on
tt2
<140
Start with no delay
DHW = on
tt2
>140
Start after 2 minute delay
DHW = on
dh
<140
Start with no delay
DHW = on
dh
>140
Start with no delay
